Magnetic field strength reduction near collector of m-type travelling wave tube



July 27, 1965 M. FAVRE MAGNETIC FIELD STRENGTH REDUCTION NEAR COLLECTOR OF M-TYPE TRAVELLING WAVE TUBE Filed March 7, 1961 uw s 2 Sheets-Sheet 1 Fig.5

INVENTOR:

MAURICE FA VRE ATTORNEYS July 27, 1965 MAGNETIC Filed March 7, 1961 M. FAVRE FIELD STRENGTH REDUCTION NEAR COLLECTOR 3,197,672 OF M-TYPE 2 Sheets-Sheet 2 Vg/ V United States Patent 3,197,672 MAGNETIC FIELD STRENGTH REDUCTION NEAR CggLECTOR OF M-TYPE TRAVELLING WAVE T E Maurice Fayre, Paris, France, assignor to 'Compagnie Generale de Telegraphie'Sans Eil, Paris, France Filed Mar. 7, 1961, Ser. No. 93,959 {Iiairns priority, applicsation lrance, Mar. 29, 1969,

9 Claims. 61. sis-39.3

The present invention relates to M-type travelling wave tubes, and more particularly to improvements in the means normally provided therefor for producing the magnetic field for M-type travelling wave tubes.

It is known already in the prior art that the M-type travelling Wave tubes operate with a magnetic field essentially perpendicular to the electric field within the interaction space of the tube and to the electron beam which propagates within this interaction space.

Within the known prior art tubes, this magnetic field is either constant all along the path of the beamexcept possibly within the area of the cathode where it has already been proposed to suppress or at least substantially reduce the action of the magnetic field on the electron gun by shielding of the latter, or by its location outside of the air gap of the magnet-or variable along this path with or without compensation of the variations in the electron speed due to these variations of the magnetic field by a correlated variation in the electric field.

In contrast to the known prior art systems, the present invention provides a device for producing the magnetic field for M-type travelling wave tubes such that the magnetic field remains essentially constant along the interaction space and undergoes an annulment or at least a sharp reduction within the area of the collector. This suppression or reduction of the magnetic field within the area of the collector causes a bending, with a constant electric field, of the trajectories of the electrons toward the collector in such a manner that the electrons may be captured or absorbed by a relatively large surface essentially parallel to the sole of the tube which improves the properties of thermal dissipation without creating, within the tube, disturbances or perturbations within the distribution of'the electric field of which any heterogeneity might lead to undesirable arcing or sparking within the tube.

The arrangement according to the presentinvention may be advantageously combined with the knownarrangement of suppression or reduction of the magnetic field within the area of the cathode. It is, therefore, preferably such that the constant magnetic field, necessary for proper operation of the tube, traverses the tube exclusively along the interaction space and be either zero or strongly weakerred outside of this space, that isat the same time within the regions of the collector and of the cathode.

The invention is realized in an advantageous manner by incorporating within the lateral walls of the tube auxiliary pole pieces supplementary to the regular magnets, these auxiliary pole pieces extending only along regions of the tube in which it is desired to maintain the non-reduced field, that is either over the entire tube except within the region of the collector or only along the interaction space to the exclusion of the regions of the collector and cathode.

In the case in which the tube under consideration isan M-type tube of circular shape, these auxiliary pole pieces will assume the form of an interrupted circular ring within the opening of which are located the collector and possibly also the cathode.

Supplementary pole pieces of similar shape and located within the space in the same manner may also be 3,197,572 Patented July 27, 1965 secured outside of the tube over the poles of the regular magnet.

According to. a modified embodiment in accordance with the present invention, a magnetic shunt may be secured to the poles of the regular magnet facing the zone of desired reduction or weakening of the magnetic field.

Accordingly, it is an object of the present invention to provide an M-type travelling wave tube, and more particularly a magnetic field source therefor which efiectively eliminates the aforementioned drawbacks and shortcomings of the prior art constructions.

It is another object of the present invention to provide a magnetic field source for M-type travelling wave tubes which effectively contributes to an increase in the capacity of the tube to dissipate heat.

A further object of the present invention resides in the provision of a source for the magnetic field of M-type travelling wave tubes which permits higher power outputs from the tube without the danger of arcing or sparking within the tube that may be caused by disturbing the electric field. i

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connectionwith the accompanying drawing, which shows in the several views thereof, for purposes of illustration only, several embodiments of the present invention as-applied to M-type circular travelling wave tubes, and wherein FIGURE 1 is an axial cross sectional view through a first embodiment in accordance with the present invention, taken along line 1-1 of FIGURE Z;

FIGURE 2 is a transverse cross sectional view of the tube illustrated in FIGURE 1, taken along line IIII thereof;

FIGURE 3 is a perspective View of an external pole piece assembly in accordance with the present invention;

FIGURE 4.isa partial axial view of a modified embodiment in accordance with the present invention, taken along line IV-IV of FIGURE 5, and

FIGURE 5 is a transverse cross sectional view taken along line VV of FIGURE 4.

Referring now to the drawing and more particularly to FIGURES 1 and 2 thereof, there may be found in these two views the usual elements of an M-type travelling wave tube of circular shape, namely anv anode ring 1 supporting thereon, in any suitable manner, a delay circuit 2 of any known construction-which extends over an arc of a circle, for example, over 270" between the ends 3 and 4 thereof. The lateral portions 5 and 6 close, in a vacuum-tight manner, the box of the tube. A sole 7 is provided within the tube, the cathode '8 being accommodated within the surface of the sole 7. Further, the tube includes a collector '9 secured to the anode ring 1. The pole pieces 10 and 11 furnish the magnetic field required for proper operation of the tube.

According to the present invention, auxiliary or supplementary pole pieces 12 and 13 are incorporated within the walls of the tube, these auxiliary pole pieces 12 and 13 having the shape of aninterrupted ring extending between the ends 14 and 15 thereof essentially in correspondence with the ends 3 and 4 of the delay circuit 2-, that is, essentially over the same arc of 270 in the illustrated embodiment. The cathode 8 and the collector 9 are therefore located within the op'eningof the interrupted ring, and the magnetic field which traverses these regions is thereby substantially weakened with respect to the field which traverses the interaction space contiguous to the 'delay circuit 2.

It follows therefore that the electrons which are supplied by cathode 8 and have traversed the interaction space,

it have the trajectories thereof bent, after leaving the interaction space at the end 14 thereof, toward the collector 9 which may therefore present a large surface essentially parallel to the sole 7 without any disturbance of the distribution of the electric field between the delay circuit 2 and the sole 7.

The effect of weakening the magnetic field within the desired regions may be further increased by securing to the poles 1t and 11 auxiliary pole pieces 16 and 17, also in the form of an interrupted ring, of which the ends 18 and 19 are brought into coincidence with the ends 14 and 15 of the delay circuit 2. FIGURE 3 illustrates in perspective the pole piece 11 having an auxiliary pole piece 17 of this type secured thereto.

The invention is applicable, in an analogous manner, to tubes of linear structure in which the auxiliary pole pieces will obviously have the shape of bars extending over any desired length of the tube. The internal pieces 12 and 13 may eventually also be dispensed with if the weakening of the magnetic field produced beyond the external pieces 16 and 17 is sufficient. 'Additionally, any other equivalent means for realizing the distribution of the magnetic field indicated hereinabove, known to a person skilled in the art, are comprised within the spirit and scope of the present invention. Among the numerous equivalent means,

one is illustrated in FIGURES 4 and 5 in which the same reference numerals are used again to designate corresponding parts as are used in connection with FIGURES 1, 2 and 3.

The illustrated assembly of FIGURES 4 and 5, with the exception of the piece 20, corresponds to a conventional circular M-type tube structure. The piece 20 is a magnetic shunt secured to the magnetic poles and 11 opposite the desired zone of reduction of the magnetic field that includes the cathode 8 and the collector 9. The action of the magnetic shunt is equivalent to the interruption in the rings 12 and 13 of FIGURES 1 and 2.

It is also understood that the arrangements of any of V the preceding figures may also be combined with the magnetic shunt of FIGURES 4 and 5.

While I have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of many changes and modifications within the spirit and scope thereof and I, therefore, do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. In a travelling wave tube of the M-type having successively adjacent an electron gun area, an interaction area and a collector area and means including pole piece meansfor generating through said three areas a transverse magnetic field, the improvement essentially consisting of means for substantially reducing the field strength of said magnetic field traversing said collector area with respect to the field strength thereof traversing said interaction area including auxiliary pole piece means operatively associated with said first-mentioned pole piece means and effectively providing discontinuities within said collector area to reduce the transverse magnetic field set up by said first-mentioned pole piece means within said collector area.

2. In a substantially circular travelling wave tube of the M-type having, along the circular contour thereof, successively adjacent an electron gun area, an interaction area and a collector area and means including main pole piece means for generating through said three areas a transverse magnetic field, the improvement essentially consisting of means for substantially reducing the field strength of said magnetic field traversing both said electron gun and collector areas with respect to the field strength thereof traversing said interaction area including auxiliary pole piece means of configuration approximately similar to and coextensive only with said interaction area to affect the iagnetic field produced by said main pole piece means within said electron gun and collector areas.

3. In a travelling wave tube of the M-type having successively adjacent an electron gun area, an interaction area and a collector area and means for generating through said three areas a transverse magnetic field, including magnetic pole pieces extending along said three areas, means for substantially reducing the field strength of said magnetic field traversing said collector area with respect to the field strength thereof traversing said interaction area including additional pole pieces extending at least along said interaction area exclusive said collector area.

4. In a travelling wave tube of the M-type having successively adjacent an electron gun area, an interaction area and a collector area and means for generating through said three areas a transverse magnetic field, including magnetic pole pieces extending along said three areas, means for substantially reducing the field strength of said mag netic field traversing said collector area with respect to the field strength thereof traversing said interaction area includingadditional pole pieces extending at least along said interaction area exclusive said collector area, said three areas being enclosed within two lateral covers of said tube essentially parallel to said pole pieces, and said additional pole pieces being secured to said covers within the tube.

5. In a travelling wave tube of the M-type provided with an electron source area, an interaction space area and a collector area, means for generating within said areas a transverse magnetic field, including magnetic pole pieces extending along said areas, and means for substan tially reducing the field strength of said magnetic field traversing the collector area in comparison to the field strength traversing said interaction area including additional pole piece means extending at least along said interaction area but exclusive of said collector area.

6. In a travelling wave tube of the M-type provided with an electron source area, an interaction space area and a collector area, means for generating within said areas a transverse magnetic field including magnetic pole pieces extending along said areas, and means for substantially reducing the field strength of said magnetic field traversing the collector area in comparison to the field strength traversing said interaction area including additional pole piece means extending at least along said interaction area but exclusive of said collector area, said additional pole piece means being fitted to said magnetic pole pieces.

7. In a circular travelling wave tube of the M-type provided with an electron source area, an interaction space area and a collector area, means for generating within said areas a transverse magnetic field including magnetic pole pieces extending along said areas, said transverse magnetic field being directed essentially along the axis thereof, and means for substantially reducing the field strength of said magnetic field traversing the collector area in comparison to the field strength traversing said interaction area including additional pole piece means extending at least along said interaction area but exclusive of said collector area, said additional pole piece means being of interrupted ring shape with the ring thereof so located that at least said collector area but excluding said interaction area essentially faces the interruption thereof.

8. In a travelling wave tube of the M-type provided, within an envelope, with an electron source area, an interaction space area and a collector area, a magnet system adapted to produce a transverse magnetic field, and means for effectively providing a field strength of said magnetic field traversing the collector area which is significantly smaller than the field strength of said field traversing said interaction area including auxiliary pole piece means within said envelope and coextensive substantially only with said interaction area to affect the magnetic field of said magnetic system.

9. In a travelling wave tube of the M-type provided with an electron source area, an interaction space area and a collector area, said three areas being enclosed between two lateral covers of the tube, magnet field generating means for generating within said areas a transverse magnetic field including magnetic pole pieces having surfaces essentially parallel to said covers and extending along said three areas, and means for substantially reducing the field strength of said magnetic field traversing the collector area with respect to the fi ld strength traversing said interaction area including first auxiliary pole piece means fitted 10 to said covers Within said tube and second auxiliary pole piece means fitted to said magnetic pole piece surfaces, said first and second auxiliary pole piece means extending at least along said interaction area exclusive of said collector area.

References Cited by the Examiner UNITED STATES PATENTS 2,745,983 5/56 Dohler et a1. 31539.3 3,027,487 4/62 Dench 315-393 3,084,279 4/63 Osepchuk 315-393 3,123,735 4/64 Hull 31539.3 X

GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, ROBERT SEGAL, Examiners. 

1. IN A TRAVELLING WAVE TUBE OF THE M-TYPE HAVING SUCCESSIVELY ADJACENT AN ELECTRON GUN AREA, AN INTERACTION AREA AND A COLLECTOR AREA AND MEANS INCLUDING POLE PIECE MEANS FOR GENERATING THROUGH SAID THREE AREAS A TRANSVERSE MAGNETIC FIELD, THE IMPROVEMENT ESSENTIALLY CONSISTING OF MEANS FOR SUBSTANTIALLY REDUCING THE FIELD STRENGTH OF SAID MAGNETIC FIELD TRAVERSING SAID COLLECTOR AREA WITH RESPECT TO THE FIELD STRENGTH THEREOF TRAVERSING SAID INTERACTION AREA INCLUDING AUXILIARY POLE PIECE MEANS OPERATIVELY ASSOCIATED WITH SAID FIRST-MENTIONED POLE PIECE MEANS AND EFFECTIVELY PROVIDING DISCONTINUITIES WITHIN SAID COLLECTOR AREA TO REDUCE THE TRANSVERSE MAGNETIC FIELD SET UP BY SAID FIRST-MENTIONED POLE PIECE MEANS WITHIN SAID COLLECTOR AREA. 